I'm going to be building a retaining box for a gravel pad using 6x6's - 0.16 lb./cu. ft. MCA pressure treated lumber. The dimensions of the box matched up with available lengths at the lumber yard, so I'm not going to have to cut any of the pieces that I've ordered. Any ends that will be below grade are going to be up against clay soil.
Do I still need to dip/paint the ends with wood preservative, or will the PT chemicals alone be sufficient to prevent rot?